Say hello to Kepler-37b: the tiniest planet ever discovered. At about one-third the diameter of Earth, Kepler-37b is about as big as our moon. It was first discovered by Thomas Barclay at the Ames Research Center in northern California using NASA's planet-hunting Kepler telescope, which simultaneously keeps an eye on 150,000 stars in the night sky for hints of new, potentially inhabitable exoplanets.

Whenever a shadow—large or small—appears in front of one of Kepler's stars, astronomers take a closer took to determine if the visual obstruction might be a previously unseen world.

Kepler-37b is one such planet. It's 210 light years away, in the constellation Lyra. It took three years for scientists to confirm that the tiny speck passing in front of its host star, Kepler-37, was indeed a floating planet all its own. Unfortunately, 37-b is also a little too close to its host star to be habitable, with surface temperatures soaring to 700 degrees Fahrenheit.

Although its discovery probably won't help sad Pluto get its planet status back anytime soon (37-b is 3,965 km across versus Pluto's 2,400 km), it does significantly raise the possibility that there are other tiny planets bouncing around the galaxy. Maybe one of these baby Earths will even fall into the Goldilocks Zone of just-right surface conditions for humans to potentially live on.